Scale embedded within hydrometer specifies that it was calibrated at 60 Deg F. The correction table provided with the hydrometer shows 0 correction at 68 Deg F and -.001 at 59 Deg F. So is the hydromter calibrated at 60 or 68?
If it says 0 correction at 68F, that's what it's calibrated to. Most that are sold for brewing is set to 60F, but I have a salt water aquarium one that is set at 68F. The 1.000 water test is the way to be sure.
I've got 2 hydrometers now and neither one of them is worth a damn. The best one reads 1.002 at 60F, the other 1.005 at 60F. (each in distilled water). However, I don't brew with distilled water so I think I will just be using this tool for very rough measurements only. I've decided that I am not going to waste any more beer taking hydrometer readings. I attached a thin/light nylon thread to the top of the best one and will simply sanitize it and lower into the carboy through the neck. I can't read it quite as accurately but the thing isn't that accurate to begin with.
Personally I'd be inclined to believe what's written inside the hydrometer rather than what's written on the scrap of paper they included with it... But it's in your best interests to check your hydrometer in distilled water anyway, so that you know if it's got any kind of inherent inaccuracy (in addition to any caused by temperature) that you need to calibrate out when taking readings - the 'calibration temperature' specified doesn't do you much good if it's not actually accurately calibrated at that temperature! If it does have an offset, you could just make yourself a new calibration table to include both the temperature calibration, and the offset.